The pregnancy zone protein serum concentration in normal pregnancy reaches its peak at about the 24th week. High serum PZ concentrations are significantly more frequent among pregnant diabetic patients without proliferative retinopathy. In contrast, the mean values in mothers with diabetes mellitus complicated by proliferative retinopathy continue to decrease. A very low limit of 150 mg/l was achieved more frequently in diabetic pregnancy complicated by fulminant proliferative retinopathy. Measurement of serum PZ levels in diabetic pregnancy might help to predict the risk of progressive retinopathy.